Gas generating materials for vehicle occupant restraints are well known. A common gas generating material comprises a thermoplastic polymeric fuel, a plasticizer for the fuel, and a finely divided particulate oxidizer. Examples of polymeric fuels are polyvinyl chloride, polyester elastomers, polyurethane elastomers, and copolymers thereof. Examples of suitable plasticizers are alkyl and alkoxy adipates, sebacates, and phthalates. Examples of suitable oxidizers are inorganic oxidizers such as ammonium, alkali metal and alkaline earth metal chlorates, perchlorates, and nitrates.
A gas generating material suitable for use in certain vehicle occupant restraints must burn fast enough to actuate the restraint, but its combustion cannot be explosive, as provided by a gun propellant.
The gas generating material is used by placing the gas generating material in a combustion chamber of a restraint apparatus. One physical form used for a gas generating material is a molded or an extruded shape, frequently in the shape of a rod. The components of the gas generating material are introduced into a forming apparatus such as a mold or an extruder. A solvent or heat may be used to facilitate mixing and extrusion. The mold or extruder produces a rod of the gas generating material which, following extrusion, is cut into suitable lengths for positioning in the combustion chamber of a restraint apparatus.
U.S. Pat. No. 660,568 discloses grooves in a rod of gas generating material to improve the burning characteristics of the gas generating material. The subject matter of this patent is a nitrocellulose based propellant for use in ordnance, and the grooves are intended to give ample vent to the gases formed on combustion of the gun propellant.
An example of an apparatus for restraining a vehicle occupant in the event of a collision is a seat belt associated with a seat belt pretensioner. The pretensioner can be actuated by a gas provided by a gas generator. The gas generator contains a body of gas generating material. The gas generator includes an igniter. The igniter is actuated to ignite the gas generating material when the vehicle experiences a collision for which pretensioning of the seat belt is desired. As the gas generating material combusts, it generates a volume of gas. The gas is directed against a mechanism, e.g. a piston, connected to a cable. The seat belt is then tightened against the vehicle occupant.